I know exactly what the noise is. It's the driveshaft contacting the front muffler. If you were to look at the driveshaft, you'd see a ring where the paint was worn away. This happens because the exhaust heats up and deflects upward when the snow hits the bottom of it. There is a tech-net note about replacing the exhaust crossmember under the area of contact to allow for more clearence. This has been an issue with all the '01 and up AWD cars. The dealer I work at was one of the first to report this to volvo. It took them a year to come up with a fix, at first they told us to bend the exhaust mounts. Now they have a new crossmember. Take it to the dealer and tell them you want it fixed. If they say it's to intermittent to pinpoint, tell them you want to speak to one of the master techs, he'll know what you're talking about.

Check the fluid level in your power steering resevoir. This happened to me last winter (in a snow storm) and likewise I thought the turbo was at fault. My symptom sounded like interference on the AM radio, passing under a hydro tower. It appears the hose was loose and allowing the fluid to escape. The dealership tightened the clamps, added power steering fluid and it has not repeated itself.
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Cam a.k.a. CVOLVO.COM

Maybe the tires were scrubbing against packed snow in the wheel-archs?